Plasma etching techniques

ABSTRACT

In certain embodiments, a method for processing a semiconductor substrate includes receiving a semiconductor substrate that includes a film stack. The film stack includes a first silicon layer, a second silicon layer, and a first germanium-containing layer positioned between the first silicon layer and the second silicon layer. The method further includes selectively etching the first germanium-containing layer by exposing the film stack to a plasma that includes fluorine agents, nitrogen agents, and hydrogen agents. The plasma etches the first germanium-containing layer and causes a passivation layer to be formed on exposed surfaces of the first silicon layer and the second silicon layer to inhibit etching of the first silicon layer and the second silicon layer during exposure of the film stack to the plasma.

TECHNICAL FIELD

This disclosure relates generally to semiconductor fabrication, and, incertain embodiments, to plasma etching techniques.

BACKGROUND

The integrated circuit (IC) manufacturing industry strives to increasedevice density to improve speed, performance, and costs. For continuedscaling to smaller node sizes, device architectures have evolved fromtwo-dimensional (2D) planar structures to three-dimensional (3D)vertical structures, such as with nanowires or vertically orientedtransistors. Insufficient control of the conducting channel by the gatepotential drives a desire for this change. Short channel effects (SCE)may become too significant as gate dimensions are scaled down and mayincrease current conduction when no voltage is applied to the gate(I_(off)). A change in device architecture may allow betterelectrostatic control of the gate to reduce the SCE and power loss.Fabricating nanowire devices may present 3D etch challenges where highlyselective isotropic etch processes are beneficial. For example, layersof exposed materials may need to be etched relative to one another tocreate indents in a film stack.

SUMMARY

In certain embodiments, a method for processing a semiconductorsubstrate includes receiving a semiconductor substrate that includes afilm stack. The film stack includes a first silicon layer, a secondsilicon layer, and a first germanium-containing layer positioned betweenthe first silicon layer and the second silicon layer. The method furtherincludes selectively etching the first germanium-containing layer byexposing the film stack to a plasma that includes fluorine agents,nitrogen agents, and hydrogen agents. The plasma etches the firstgermanium-containing layer and causes a passivation layer to be formedon exposed surfaces of the first silicon layer and the second siliconlayer to inhibit etching of the first silicon layer and the secondsilicon layer during exposure of the film stack to the plasma.

In certain embodiments, a method for processing a semiconductorsubstrate includes positioning a semiconductor substrate in a plasmachamber of a plasma tool. The semiconductor substrate includes a filmstack that has silicon layers and germanium-containing layers in analternating stacked arrangement, with at least two silicon layers and atleast two germanium-containing layers. The method further includesgenerating, in the plasma chamber of the plasma tool, a plasma thatincludes fluorine agents, nitrogen agents, and hydrogen agents. Theplasma is generated from gases that include a fluorine-containing gas, anitrogen-containing gas, a hydrogen-containing gas, and a noble gas. Themethod further includes exposing, in the plasma chamber of the plasmatool, the film stack to the plasma. The plasma causes a nitridepassivation layer to be formed on exposed surfaces of the silicon layersand selectively etches opposing exposed ends of the germanium-containinglayers to form indents in the germanium-containing layers relative toopposing exposed ends of the silicon layers. The nitride passivationlayer inhibits etching of the silicon layers by the plasma.

In certain embodiments, a method for processing a semiconductorsubstrate includes positioning a semiconductor substrate in a plasmachamber of a plasma tool. The semiconductor substrate includes a filmstack that has first layers of a first material and second layers of asecond material in an alternating stacked arrangement. The firstmaterial is a germanium-containing material that includes germanium at aconcentration of about ten to about fifty percent. The method furtherincludes generating a plasma for selectively etching the first layers ofthe first material. Generating the plasma includes introducing gasescontaining fluorine, nitrogen, hydrogen, and a noble gas into the plasmachamber and maintaining a pressure in the plasma chamber of less thanabout 50 millitorr. The method further includes exposing, in the plasmachamber, the film stack to the plasma for a time period. The plasmaselectively etches opposing exposed ends of the first layers of thefirst material to form indents in the first layers of the first materialrelative to opposing exposed ends of the second layers of the secondmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, and advantagesthereof, reference is made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIGS. 1A-1D illustrate cross-sectional views of an example semiconductorsubstrate during an example process for processing the semiconductorsubstrate, according to certain embodiments of this disclosure;

FIG. 2 illustrates an example method for processing a semiconductorsubstrate, according to certain embodiments of this disclosure;

FIG. 3 illustrates an example method for processing a semiconductorsubstrate, according to certain embodiments of this disclosure;

FIG. 4 illustrates an example device including a substrate with arecessed alternating film stack, according to certain embodiments ofthis disclosure; and

FIG. 5 illustrates a block diagram of an example plasma tool, accordingto certain embodiments of this disclosure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Various techniques for attempting to selectively etch one materialrelative to another exist. In some cases the chemistry of two materialsis sufficiently distinct to allow a plasma that is selective to etchingone of the materials to be used without concern for etching the othermaterial. In other cases determining appropriate etching regimes forselective etching is more difficult because the chemistry of thematerials may be similar or the available etching processes may belimited by other factors. Certain materials present more difficultselectivity challenges where it is desirable to etch one material withlittle to no etching of another material. Conventional processes forthis type of selective etching may be unable to achieve selectiveetching of one material relative to another or may fall short of processrequirements such as selectivity, etch profile (e.g., local uniformityand/or surface roughness), and others.

Selectivity challenges may arise in forming nanowires or nanosheets toact as a channel region in a 3D vertical structure of a semiconductordevice, such as a gate-all-around (GAA) device. Forming such nanowiresmay involve forming a film stack on a base layer, the film stackincluding layers of Si and Ge or Si—Ge (SiGe) alloy arranged in analternating stack. Part of this process may include etching indents inthe film stack at opposing ends of the Ge or Ge-containing layers, whileminimizing etching of the silicon (Si) layers, to expose end portions ofthe Si layers for later use as a conducting device. Due to variouschallenges, including in part a native oxide layer (NOL) and/or otherresidues (e.g., reactive ion etching (RIE) residue) present on surfacesof the film stack, conventional etching techniques maybe unsatisfactory.

Etching Ge-containing layers while also minimizing etching of the Silayers may be particularly challenging when the Ge-containing layersinclude a relatively low concentration of Ge, such as less than or equalto about 30% Ge and, in a particular example, less than or equal toabout 15%. This challenge may be due, at least in part, to the chemicalmake-up of the Ge-containing layers (e.g., SiGe layers) and to the Silayers becoming more similar when Ge-containing layers having lowerconcentrations of Ge are used.

Prior to performing the plasma etch to form indents in the film stack,some conventional techniques use a wet or dry process to remove the NOL.The film stack may be processed using a dilute hydrogen-fluoride (HF)acid or a chemical oxide removal process with the formation of ammoniumfluorosilicate. Removing the NOL over surfaces of both the Si layers andthe Ge-containing layers, however, may reduce the selectivity of thesubsequent indent plasma etch process (e.g., using a conventionalfluorine-based etch process, as described below) to etch theGe-containing layers with minimal to no etching of the Si layers.

Some conventional techniques expose surfaces of both the Si layers andthe Ge-containing layers (e.g., along the sidewalls of the film stack)to fluorine-containing chemicals (e.g., fluorine (F₂), chlorinetrifluoride (ClF₃), bromine trifluoride (BrF₃), or iodine pentafluoride(IF₅)) or to fluorine-containing radicals generated by plasma. Suchconventional plasmas may be generated from gases including carbontetrafluoride (CF₄) and argon (Ar) or from gases including nitrogentrifluoride (NF₃) and nitrogen (N₂). The fluorine-containing etchants(whether in the fluorine-containing chemicals or fluorine radicals in aplasma) may react more quickly with the Ge-containing layers than the Silayers, which may achieve some level of selectivity to Si (etching theGe-containing layers faster than the Si layers). While the Si layers areless reactive to the fluorine-containing etchants associated with theseconventional techniques, an undesirable amount of etching of the Silayers still occurs. For example, the etching of the Si layers canresult in corner rounding if the etching of the Si layers occurs at thecorners of the Si layers. Additionally, at relatively low concentrationsof Ge in the Ge-containing layers (e.g., ≤about 30%, and ≤about 15% in aparticular example), the difference in reactivity of the Si layers andthe Ge-containing layers to the fluorine-containing etchants may besignificantly reduced, which may lead to poor selectivity (e.g., lessthan about 20:1 (etch rate of the Ge-containing layers to the etch rateof the Si layers) for 15% Ge in a particular example).

Embodiments described below provide various techniques of selectiveetching. For example, embodiments may be used to selectively etchportions of a film stack (e.g., that includes Si layers andGe-containing layers in an alternating stacked arrangement) of asubstrate. It may be desirable to selectively etch indents in edgeportions of (or possibly completely remove) the Ge-containing layers toform the contact handles for Si nanowire layers and may provide improvedselectivity to Si layers even at low concentrations of Ge in theGe-containing layers (e.g., less than about 50% Ge, less than about 30%Ge, less than about 25% Ge, and in particular embodiments less thanabout 15% Ge).

Certain embodiments use plasma to form indented regions, or recesses, ina film stack that includes Si layers and Ge-containing layers in analternating stacked arrangement. The plasma may be generated from gasesthat include a fluorine-containing gas, a hydrogen-containing gas, and acarrier gas (e.g. noble gases such as Ar and He), and the plasma mayinclude fluorine agents, hydrogen agents, and nitrogen agents. Theplasma may cause a passivation layer (e.g., a nitride passivation layer,such as a Si nitride passivation layer) to be formed on exposed surfacesof the Si layers, which may serve as an etch stop layer on exposedsurfaces of the Si layers while the etchant in the plasma (e.g.,fluorine agents) etches the Ge-containing layers. Prior to exposing thesubstrate to the plasma, a barrier layer (e.g., an NOL) may besubstantially removed from exposed surfaces of the film stack using asuitable dry or wet etch process.

FIGS. 1A-1D illustrate cross-sectional views of an example substrate 102during an example process 100 for processing substrate 102, according tocertain embodiments of this disclosure. In certain embodiments, process100 includes using a plasma suitable for etching portions of certainlayers (e.g., Ge-containing layers) of a film stack of substrate 102while forming a protective passivation layer on exposed portions ofother layers (e.g., Si layers) of the film stack, resulting in substrate102 having an indented film stack following execution of process 100.

As illustrated in FIG. 1A, substrate 102 is a semiconductor substratethat includes film stack 104 disposed on a base layer 106. Film stack104 includes Ge-containing layers 108 and Si layers 110 in analternating stacked arrangement. Film stack 104 may have any suitableshape and include any suitable number of layers. As examples, thevertical thickness of individual Ge-containing layers 108 and Si layers110 may be about 5 nm to about 25 nm each, and as particular examplesmaybe about 10 nm or about 20 nm. Additionally, Ge-containing layers 108may have the same thicknesses or may vary in thickness relative to oneanother, Si layers 110 may have the same thickness or may vary inthickness relative to one another, and Ge-containing layers 108 and Silayers 110 may have the same thicknesses or may vary in thicknessrelative to one another. In a particular example, Ge-containing layers108 and Si layers 110 all have substantially the same thicknesses.

The material of Ge-containing layers 108 may be pure Ge or SiGe alloy,for example. As a particular example, the Ge-containing layers 108 mayinclude a SiGe alloy (mixture) in an appropriate ratio (e.g.,Si_(0.7)Ge_(0.3), Si_(0.85)Ge_(0.15), etc.) for desired etchingproperties of a given application or for desired performance in aresulting semiconductor device formed using, in part, process 100.Although this disclosure contemplates Ge-containing layers 108 includingany suitable concentration of Ge (including 100% Ge) relative to anothermaterial (e.g., Si), in certain embodiments Ge-containing layers 108including less than or equal to about 50% Ge, less than or equal toabout 30% Ge, less than or equal to about 25% Ge, less than or equal toabout 15% Ge, or less than or equal to about 10% Ge. As just oneparticular example range, Ge-containing layers 108 may include about 10%to about 50% Ge relative to another one or more materials (e.g., Si). Incertain embodiments, all Ge-containing layers 108 include the samematerials; however, Ge-containing layers 108 may include differentmaterials if desired.

The material of Si layers 110 may be pure Si, for example. In certainembodiments, all Si layers 110 include the same material; however, Silayers 110 may include different materials if desired. Although in thisparticular example Si layers 110 are primarily described as being pureSi, it should be understood that in certain embodiments, the materialselective to which Ge-containing layers (e.g., Ge-containing layers 108)are being etched may include another suitable material such as Sinitride (SiN).

Base layer 106 may be any suitable material and is or includes Si in oneexample. In a particular example, film stack 104 is formed by growingalternating heteroepitaxial layers of Ge or SiGe (e.g., Ge-containinglayers 108) and Si (e.g., Si layers 110) atop base layer 106.

An optional hard mask 112 may be included on top of film stack 104. Hardmask 112 may have been used to form the structure of film stack 104, ina previous etch process for example. In certain embodiments, hard mask112 is SiN (e.g., Si nitride (Si₃N₄)) but may include any suitablematerial.

A barrier layer 114 is formed over film stack 104 (including hard mask112) and, in this example, base layer 106. Barrier layer 114 may resultfrom prior fabrication steps (e.g., RIE) applied to substrate 102 orfrom other handling of substrate 102 (e.g., exposure to ambient air whentransferring between processing tools). As particular examples, barrierlayer 114 may include an NOL, RIE residue, or both. An NOL may be a thinlayer of SiO₂ (or other suitable material), about 1.0 nm to about 2.0 nmthick for example, that forms on surfaces of substrate 102, such as whensubstrate 102 is exposed to ambient air, which contains O₂ and H₂O. Forexample, surfaces of base layer 106, Ge-containing layers 108, Si layers110, and hard mask 112 may interact with the ambient air, which mayresult in barrier layer 114 at those surfaces. As another example,surfaces of base layer 106, Ge-containing layers 108, Si layers 110, andhard mask 112 may include a residue resulting from prior RIE steps.

Barrier layer 114 may have different etch properties than layers thatunderlie barrier layer 114. Although shown as having generally uniformcoverage over film stack 104 (including hard mask 112) and base layer106, barrier layer 114 might or might not have uniform coverage.

Each of the layers in film stack 104 has a pair of exposed surfaces atopposed ends when viewed, as illustrated, from a cross-sectionalperspective. That is, each of Ge-containing layers 108 has (opposing)exposed surfaces 116, and each of Si layers 110 has (opposing) exposedsurfaces 118. Additionally, in the state illustrated in FIG. 1A, becausesubstrate 102 includes barrier layer 114, exposed surfaces of 116 ofGe-containing layers 108 and exposed surfaces 118 of Si layers 110include barrier layer 114.

As illustrated in FIG. 1B, barrier layer 114 is etched to remove some orall of barrier layer 114 from exposed surfaces 116 of Ge-containinglayers 108, from exposed surfaces 118 of Si layers 110, and from exposedsurfaces of base layer 106 and hard mask 112. Barrier layer 114 mayberemoved using any suitable process, including any suitable wet etch ordry etch process. In certain embodiments, substrate 102 is processedusing a dilute HF acid or a chemical oxide removal process to removesome or all of barrier layer 114. The process used to etch barrier layer114 might or might not remove some or all of hard mask 112, but forpurposes of this example, hard mask 112 is shown not to be removed orotherwise etched. Removing barrier layer 114 from exposed surfaces 116of Ge-containing layers 108 and from exposed surfaces 118 of Si layers110, however, may reduce the selectivity of a subsequent conventionalfluorine-based indent plasma etch process to attempt to etchGe-containing layers 108 with minimal to no etching of Si layers 110.

As illustrated in FIG. 1C, in a plasma step 120 of process 100,substrate 102 is exposed to plasma 122 to selectively etch Ge-containinglayers 108. For example, substrate 102 may be exposed to plasma 122 toselectively etch exposed surfaces 116 of Ge-containing layers 108 toform indents 136 in film stack 104, with opposing end portions ofGe-containing layers 108 in an intermediate state of removal/etchingrelative to adjacent Si layers 110. In certain embodiments, plasma step120 is an isotropic etch process.

Plasma step 120 may be performed in plasma chamber 123 of a plasma tool.The plasma tool may be any suitable type of plasma tool, including aninductively-coupled plasma (ICP) tool, a capacitively-coupled plasma(CCP) tool, a surface wave plasma (SWP) tool, and others. One exampleplasma tool is described below with reference to FIG. 5.

During exposure of substrate 102 to plasma 122 and to facilitateselective etching of Ge-containing layers 108, plasma 122 may cause apassivation layer 124 to be formed on exposed surfaces 118 of Si layers110. Plasma 122 may cause passivation layer 124 to form on exposedsurfaces 118 of Si layers 110 by removing and replacing or otherwisemodifying portions of Si layers 110 at exposed surfaces 118 of Si layers110. In certain embodiments, passivation layer 124 also maybe formed onexposed surfaces of base layer 106, such as when base layer 106 is pureSi or is Si nitride.

During exposure of substrate 102 to plasma 122, passivation layer 124 onexposed surfaces 118 of Si layers 110 (and, in the illustrated example,on exposed surfaces of base layer 106) inhibits etching of Si layers 110(and, in the illustrated example, of base layer 106). In other words,plasma 122 selectively etches Ge-containing layers 108 due at least inpart to the formation and presence of passivation layer 124 on exposedsurfaces 118 of Si layers 110 (and on exposed surfaces of base layer106), passivation layer 124 acting as an etch stop layer on exposedsurfaces 118 of Si layers 110 (and on exposed surfaces of base layer106). In certain embodiments, passivation layer 124 inhibiting etchingof Si layers 110 (and, in the illustrated example, of base layer 106)includes passivation layer 124 preventing etching of some or all of Silayers 110, reducing etching of some or all of Si layers 110, slowingdown etching of some or all of Si layers 110, or the like.

Although passivation layer 124 may have any suitable thickness, incertain embodiments, passivation layer 124 is relatively thin, such as 2nm or less. Passivation layer 124 could be, for example, a monolayer. Incertain embodiments, passivation layer 124 is a nitride, such as Sinitride (e.g., Si₃N₄).

As plasma 122 etches Ge-containing layers 108, additional surfaces 138of Si layers 110 are exposed. That is, as indents 136, or recesses, areformed in film stack 104 due to the selective etching of Ge-containinglayers 108, additional surfaces 138 of Si layers 110 are exposed. Plasma122 may continue to form passivation layer 124 on additional surfaces138. Passivation layer 124 formed on additional surfaces 138 also maybea nitride, such as Si nitride (e.g., Si₃N₄). In other words, passivationlayer 124 is further formed over newly exposed surfaces (e.g.,additional surfaces 138) of Si layers 110 as Ge-containing layers 108are etched above, below, and/or between Si layers 110. Passivation layer124 on additional surfaces 138 inhibits etching of Si layers 110 atadditional surfaces 138, while passivation layer 124 at exposed surfaces118 of Si layers 110 inhibits etching of Si layers 110 at exposedsurfaces 118.

Plasma 122 may include fluorine agents 126, hydrogen agents 128, andnitrogen agents 130. Fluorine agents 126 may act primarily as theetchant for etching Ge-containing layers 108 at exposed surfaces 116 ofGe-containing layers 108. Hydrogen agents 128 may act as a reducingagent, facilitating the etching of Ge-containing layers 108 at exposedsurfaces 116 of Ge-containing layers 108 in the presence of fluorineagents 126. Furthermore, if applicable depending on the gases used togenerate plasma 122, hydrogen agents 128 may further break down certaincompounds of fluorine and nitrogen to produce fluorine agents 126 andnitrogen agents 130, and to promote formation of passivation layer 124(e.g., nitrides, such as Si nitride) on surfaces 118 of Si layers 110and/or etching of Ge-containing layers 108. Nitrogen agents 130 reactwith the Si at exposed surfaces 118 of Si layers 110 to form a nitridelayer (e.g., a Si nitride layer, such as Si₃N₄) at exposed surfaces 118.For example, the atomic nitrogen (N) generated in plasma 122 may reactwith the Si molecules at exposed surfaces 118 of Si layers 110 (andexposed surfaces of base layer 106) to form passivation layer 124 (e.g.,a nitride layer) on exposed surfaces 118 of Si layers 110 (and onexposed surfaces of base layer 106).

Although fluorine agents 126, hydrogen agents 128, and nitrogen agents130 are primarily illustrated and described as separate elements, thisdisclosure contemplates fluorine agents 126, hydrogen agents 128, andnitrogen agents 130 being separate or some or all of fluorine agents126, hydrogen agents 128, and nitrogen agents 130 being part of one ormore compounds within plasma 122. For example, plasma 122 may includeone or more of NH species, HF species, NF species, or other suitablespecies. It will be understood that references throughout thisdisclosure to fluorine agents 126, hydrogen agents 128, and nitrogenagents 130 contemplates these agents as separate elements and theseagents as part of one or more compounds of plasma 122.

In certain embodiments, plasma 122 may be generated from gases thatinclude fluorine-containing gas, hydrogen-containing gas,nitrogen-containing gas, and a noble gas. The fluorine-containing gasmay act as an etchant, the hydrogen-containing gas may act as areductive gas, and the noble gas may act as a carrier gas. As a fewexamples, a fluorine-containing gas that is used to generate plasma 122may include NF₃, sulfur hexafluoride (SF₆), or carbon tetrafluoride(CF₄). In certain embodiments, such as some examples in which afluorine-containing gas that does not include nitrogen is used (or evenin some examples in which a fluorine-containing gas that does includenitrogen is used), it may be appropriate to provide nitrogen gas inanother suitable way, such as by introducing ammonia (NH₃), which alsomight be used as the hydrogen-containing gas as described below, ornitrogen gas (N₂). Regarding the hydrogen-containing gas, as a fewexamples, a hydrogen-containing gas that is used to generate plasma 122may include H₂ or ammonia (NH₃). As described above, the hydrogen gasmay promote formation of passivation layer 124 (e.g., nitrides, such asSi nitride) on surfaces 118 of Si layers 110 and/or etching ofGe-containing layers 108.

Although illustrated separately, the nitrogen-containing gas might beprovided separately (e.g., as nitrogen gas (N₂)) and/or as part of acompound with one or more of the other gases used to generate plasma 122(e.g., as part of a compound with the fluorine-containing gas and/or aspart of a compound with the hydrogen-containing gas). For example, anitrogen carrier gas (N₂) may be added and/or the nitrogen agents 130for forming passivation layer 124 (e.g., in embodiments in whichpassivation layer 124 is a nitride layer) may be provided from othergases, such as a nitrogen-containing compound for thefluorine-containing gas or a nitrogen-containing compound for thehydrogen-containing gas. In other words, the source of nitrogen agents130 in plasma 122 may be an etchant gas (e.g., a fluorine-containinggas) that includes nitrogen (e.g., NF₃), a reductive gas (e.g., ahydrogen-containing gas) that includes nitrogen (e.g., NH₃), a carriergas that includes nitrogen (e.g., an N₂ carrier gas), or anothersuitable nitrogen-containing source gas, and nitrogen agents 130 maybeatomic nitrogen disassociated from the source gas.

As a particular example, the gases used to generate plasma 122 mayinclude a suitable combination of NF₃, Ar, and H₂. In certainembodiments, the Ar could be replaced by another noble gas, such ashelium (He) or krypton (Kr). As particular examples, gases/gascombinations used to generate plasma 122 may include NF₃/NH₃/Ar,NF₃/NH₃/N₂/Ar, NF₃/H₂/Ar, or NF₃/H₂/Ar/N₂.

Various process parameters for plasma step 120 may be optimized topromote formation of fluorine agents 126 for effective etching ofGe-containing layers 108 while generating sufficient hydrogen agents 128and nitrogen agents 130 for forming passivation layer 124 (e.g., anitride passivation layer, such as Si nitride) at exposed surfaces 118and additional surfaces 138 of Si layers 110. In an example in which thegases used to generate plasma 122 include NF₃ and H₂, the ratio of NF₃to H₂ may be an appropriate consideration. The ratio of one gas toanother may be measure in terms of respective flow rates, such asstandard cubic centimeters per minute (sccm). In certain embodiments,plasma 122 includes more fluorine agents 126 than hydrogen agents 128 toensure that Ge-containing layers 108 are still etched and that apassivation layer similar to passivation layer 124 is unlikely to formon exposed surfaces 116 of Ge-containing layers 108 (particularly at lowconcentrations of Ge in Ge-containing layers 108), but also includessufficient nitrogen agents 130 and hydrogen agents 128 to facilitateformation of passivation layer 124 sufficiently quickly to reduce oreliminate etching of Si layers 110 by the generally more reactivefluorine agents 126.

The appropriate ratio (or range of ratios) may depend on a variety offactors, including other process parameters and the concentration of Gein Si layers 110. Hydrogen gas (H₂) may help drive the reactionsoccurring in plasma chamber 123, including etching of Ge-containinglayers 108 and formation of passivation layer 124 on exposed surfaces118 and additional surfaces 138 of Si layers 110. Example ranges for theratio of NF₃ to H₂ may include from NF₃:H₂=about 4:about 1 toNF₃:H₂=about 10:about 1, and maybe NF₃:H₂=about 5:about 1 in aparticular example. In certain embodiments, when the H₂ low is higherthan about 30 seem and the concentration of Ge in Ge-containing layers108 is less than or equal to about 15%, then the etch rate ofGe-containing layers 108 by fluorine agents 126 may be reduced. Itshould be understood that this may or may not be the case for certainimplementations, as the particular etch rates can depend on a variety offactors. Regarding the noble gas, example ranges for the ratio of NF₃ toAr may include from NF₃:Ar=about 1:about 2.5 to NF₃:Ar=about 1:about 10.

Other process parameters for generating plasma 122 include gas flowrates, pressure, plasma source power, plasma bias power, time, andtemperature. The gases for forming plasma 122 may be provided at anysuitable flow rate. In certain embodiments, the etchant source gas flowrate is fluorine-containing gas (e.g., NF₃)=20-80 seem (and 50 seem in aparticular example), H₂=5-15 seem (and 10 seem in a particular example),Ar=500-1500 seem (and 1000 seem in a particular example). In theseexamples, the flow rate of the fluorine-containing gas is relativelymoderate, the flow rate of the hydrogen-containing gas is relativelylow, and the flow rate of the noble gas is relatively high.

In certain embodiments, plasma step 120 may be performed at relativelylow pressure (e.g., less than about 100 mTorr, less than about 50 mTorr,and in one example about 15 mTorr to about 25 mTorr) and at relativelylow source power (e.g., less than about 400 W, less than about 100 W,and in one example a high frequency source power of about 100 W and alow frequency bias power of about 0 W). Exposure time for plasma step120 may be any suitable time. In certain embodiments, exposure timecould be as little as about five seconds or less, fifteen seconds orless, twenty-five seconds or less, thirty seconds or less, or 45 secondor less. The appropriate exposure time may depend on other parameterssuch that the optimum combination of parameters is determined to achievethe desired level of selectivity (or other appropriate goals). Incertain embodiments, plasma step 120 is performed at a temperature ofapproximately −40° C. to approximately 20° C., and in one example atabout ° C.

One example recipe for plasma step 120 includes the following: pressureabout 15 to about 25 mTorr; source power (inductively coupled plasma)100 W; bias power 0 W; wafer processing temperature 0° C.; and NF₃, H₂,and Ar flow rates of 50 sccm, 10 sccm, and 1000 sccm, respectively.

It should be understood that as to all parameters described herein,particular values and ranges are provided for example purposes only.

In certain embodiments, plasma step 120 is an oxygen-free plasma etchstep to etch portions of certain layers of a film stack of substrate102, resulting in substrate 102 having an indented, or recessed, filmstack following execution of process 100. It should be understood thatoxygen-free does not necessarily mean that all oxygen is eliminated fromplasma step 120, but instead reflects that oxygen-containing gas is notdeliberately introduced as part of plasma step 120. Removing all oxygenfrom a plasma chamber 123 may be difficult or impossible, so some oxygenmay still be present in plasma chamber 123 during plasma step 120.

FIG. 1D illustrates substrate 102 following plasma step 120. In thestate illustrated in FIG. 1D, film stack 104 includes indents 136 (ofwhich two examples are labeled). Furthermore, due to the formation ofindents 136, exposed ends 141 (of which one example is labeled) of Silayers 110 may be formed.

FIG. 1D shows certain measurements of resulting substrate 102, such asexposed end separation 142 and etched width 144. For example, exposedend separation 142 shows the remaining width (per this cross-section) ofGe-containing layers 108 by measuring each Ge-containing layer 108 froma first exposed surface 116 on a first side of film stack 104 to anopposing second exposed surface 116 on a second side of film stack 104.Exposed end separation 142 may be less than about 20 nm in certainembodiments, and between about 2 nm and about 20 nm in one embodiment.The exposed end separation may also refer to the separation of exposedends prior to etching. Etched width 144 may measure how much of aparticular Ge-containing layer 108 was removed from a particular end ofthe particular Ge-containing layer 108. In other words, etched width 144may measure the amount of an indent 136 of a Ge-containing layer 108. Incertain embodiments, etched width 144 is about 5 nm to about 50 nm.However, exposed end separation 142 and etched width 144 may be outsidethese ranges depending on a given application.

Subsequent processing may then be performed on substrate 102. Forexample, plasma step 120 may be integrated into a process for forming Silayers 110 into respective nanowires for a channel region of asemiconductor device, such as a GAA or other 3D device. In such adevice, subsequent processing may include filling the indents 136 withan insulator, removing remaining portions of Ge-containing layers 108,providing a gate oxide around Si layers 110, and other associated steps,all of which are provided for example purposes only. In such a device,exposed ends 141 of Si layers 110 may serve as conductive contacts to achannel region formed in the area of film stack 104.

Process 100 may provide one or more technical advantages. Someconventional techniques for attempting to etch Ge-containing layers 108selective to Si layers 110 expose surfaces of both Si layers 110 (e.g.,exposed surfaces 118 and additional surfaces 138) and Ge-containinglayers 108 (e.g., exposed surfaces 116) (e.g., along the sidewalls offilm stack 104) to fluorine-containing chemicals (e.g., F₂, ClF₃, BrF₃,or IF₅) or fluorine-containing radicals generated by plasma. Suchconventional plasmas, for example, may be generated from gases includingCF₄ and Ar or from gases including NF₃ and N₂. The fluorine-containingetchants (whether in the fluorine-containing chemicals or fluorineradicals in a plasma) may react more quickly with Ge-containing layers108 than Si layers 110, which may achieve some level of selectivity toSi (etching Ge-containing layers 108 faster than Si layers 110);however, an undesirable amount of etching of Si layers 110 still occurs.

For example, the etching of Si layers 110 can result in corner roundingif the etching of Si layers 110 occurs at the corners of Si layers 110.Additionally, a vertical thickness of Si layers 110 may be reduced by anundesirable amount, particular toward exposed surfaces 118, which areexposed to the etchant for the longest amount of time as exposedsurfaces 116 of Ge-containing layers 108 are etched inward to formindents 136. Furthermore, at relatively low concentrations of Ge inGe-containing layers 108 (e.g., ≤about 30%, and ≤about 15% in aparticular example), the difference in reactivity of Si layers 110 andGe-containing layers 108 to the fluorine-containing etchants may besignificantly reduced, which may lead to poor selectivity (e.g., lessthan about 20:1 (etch rate of the Ge-containing layers to the etch rateof the Si layers)).

Additionally, conventional fluorine-based plasmas may etch othermaterials on a semiconductor substrate, such as Si dioxide (SiO₂), Sinitride (Si₃N₄), oxides, and low-k dielectric materials, which may beundesirable. In other words, such conventional fluorine-based plasmasare not selective to SiO₂, Si₃N₄, oxides, and low-k dielectric materials(e.g., Si oxycarbonitride (SiOCN), Si boron carbonitride (SiBCN), etc.).

According to embodiments of process 100, plasma step 120 may includeforming passivation layer 124 (e.g., a nitride such as Si nitride) on Silayers 110. Passivation layer 124 inhibits etching of Si layers 110(e.g., exposed surfaces 118 and additional surfaces 138) while theetchant of plasma 122 (e.g., fluorine agents 126) etch Ge-containinglayers 108 to form indents 136 in film stack 104. In certainembodiments, despite a potentially low concentration of Ge inGe-containing layers 108 (e.g., less than about 50%, less than about30%, less than about 25%, and less than about 15% in a particularexample), and depending in part on the concentration of Ge inGe-containing layers 108, the selectivity (as measured by respectiveetch rates) of Ge-containing layers 108 to the Si layers 110 is greaterthan or equal to about 50 to about 1, greater than or equal to about 70to about 1, or greater than or equal to about 100 to about 1. It shouldbe understood that the respective etch rates can be determined in anysuitable manner.

Additionally, due at least in part to the high-selectivity of plasma 122to Si layers 110, which itself maybe due at least in part to rapidformation of passivation layer 124 on exposed surfaces 118 andadditional surfaces 138 of Si layers 110, film stack 104 may have animproved etch profile. The improved etch profile may include reducedsurface roughness along surfaces 116 of Ge-containing layers 108 (to theextent Ge-containing layers 108 are not completely removed) and, inparticular, along exposed surfaces 118 and remaining surfaces 138 of Silayers 110 following plasma step 120. Additionally or alternatively, theimproved etch profile may include improved sharpness edges and arelatively square-shaped profile of exposed ends 141 of Si layers 110following plasma step 120 as compared to what was possible withconventional techniques. In certain embodiments, plasma step 120,including the use of plasma 122 provides a relatively straight etchfront along surfaces 116 of Ge-containing layers 108 (to the extentGe-containing layers 108 are not completely removed) and good localuniformity regarding the amount of material removed from eachGe-containing layer 108 of film stack 104.

The nitride (e.g., Si nitride) passivation layer 124 may be insoluble inwater, allowing passivation layer 124 to act as an O₂ and H₂O diffusionbarrier and thereby improve the stability of the nanowire formed fromthe Si layer 110. In addition to being selective to Ge and SiGe, plasma122 (e.g., a fluorine-, hydrogen- and nitrogen-containing plasma) alsomaybe selective to SiO₂, Si₃N₄, oxides, and low-k dielectric materials(e.g., SiOCN, SiBCN, etc.) due to the absence, in certain embodiments,of oxygen in the chemistry which is typically present for removingcarbon and nitrogen bonds in these compounds (e.g., SiO₂, Si₃N₄, oxides,and low-k dielectric materials (e.g., SiOCN, SiBCN, etc.).

Furthermore, certain embodiments may provide improved structures thatcan be used in 3D devices such as may be suitable for GAA devices, 3DNAND or other memory devices, logic devices, or any other suitable typeof semiconductor device.

FIG. 2 illustrates an example method 200 for processing substrate 102,according to certain embodiments of this disclosure. Method 200 beginsat step 202. At step 204, substrate 102 is received. Substrate 102 hasfilm stack 104 that includes Ge-containing layers 108 and Si layers 110in an alternating stacked arrangement. That is, film stack 104 mayinclude alternating Ge-containing layers 108 and Si layers 110 (e.g., asillustrated in FIG. 1A). Barrier layer 114 (e.g., an NOL) may be presenton surfaces of film stack 104, such as on exposed surfaces 116 ofGe-containing layers 108, exposed surfaces 118 of Si layers 110, andexposed surfaces of base layer 106 and hard mask 112.

At step 206, barrier layer 114 on surfaces of film stack 104 is etchedto remove barrier layer 114, from exposed surfaces 116 of Ge-containinglayers 108, from exposed surfaces 118 of Si layers 110, and from exposedsurfaces of base layer 106 and hard mask 112, for example. Barrier layer114 maybe removed using any suitable process (e.g., a wet etch or dryetch process).

At step 208, Ge-containing layers 108 are selectively etched by exposingsubstrate 102 (including film stack 104) to plasma 122. Plasma 122 mayinclude fluorine agents 126, hydrogen agents 128, and nitrogen agents130. Plasma 122 etches Ge-containing layers 108 and causes passivationlayer 124 to be formed on exposed surfaces 118 of Si layers 110 toinhibit etching of Si layers 110 during exposure of semiconductor device102 (including film stack 104) to plasma 122. In certain embodiments,step 208 is an isotropic etch process.

In certain embodiments, plasma 122 is generated from gases that includeNF₃ gas, and fluorine agents 126 include fluorine disassociated from theNF₃ gas. In an example, nitrogen agents 130 include nitrogendisassociated from the NF₃ gas. In certain embodiments, plasma 122 isgenerated from gases that include H₂ gas, and hydrogen agents 128include hydrogen. In certain embodiments, plasma 122 is generated fromgases that include at least one noble gas, such as Ar, He, or Kr. Asparticular examples, plasma 122 may be generated from a gas combinationthat includes NF₃, NH₃, and Ar; NF₃, NH₃, N₂, and Ar; NF₃, H₂, and Ar;or NF₃, H₂, Ar, and N₂. In certain embodiments, passivation layer 124formed on exposed surfaces 118 of Si layers 110 includes Si nitride(e.g., Si₃N₄).

Selectively etching Ge-containing layers 108 may include selectivelyetching end portions of Ge-containing layers 108 to form indents 136 infilm stack 104 above, below, or between Si layers 110. As Ge-containinglayers 108 are selectively etched, additional surfaces 138 of Si layers110 are exposed, and plasma 122 forms passivation layer 124 onadditional surfaces 138. In certain embodiments, selectively etchingGe-containing layer 108 includes selectively removing substantially allof Ge-containing layers 108 such that Si layers 110 are released.

In certain embodiments, one or more of the Ge-containing layers 108 areSiGe layers that includes about fifty percent or less Ge. In a moreparticular embodiment, one or more of the Ge-containing layers 108include less than or equal to about fifteen percent Ge, and theselectivity (as measured by respective etch rates) of the one or morefifteen percent Ge-containing layers 108 to the Si layers 110 is greaterthan or equal to about 70:1.

At step 210, additional fabrication steps are executed. The discussionof potential additional processing steps described above with referenceto FIG. 1D is incorporated by reference. For example, in certainembodiments, step 208 is integrated into a process for forming Si layers110 into respective nanowires for a channel region of a semiconductordevice, such as a GAA device. At step 212, the method ends.

FIG. 3 illustrates an example method 300 for processing substrate 102,according to certain embodiments of this disclosure. Method 300 beginsat step 302. A step 304, substrate 102 is positioned in plasma chamber123 of a plasma tool. Substrate 102 has film stack 104 that includesGe-containing layers 108 and Si layers 110 in an alternating stackedarrangement (e.g., as shown in FIG. 1A).

At step 306, plasma 122 is generated in plasma chamber 123 of the plasmatool. Plasma 122 includes fluorine agents 126, hydrogen agents 128, andnitrogen agents 130. Plasma 122 may be generated from gases that includea fluorine-containing gas, such as NF₃, SF₆, or CF₄. Fluorine agents 126may include fluorine disassociated from the fluorine-containing gas. Incertain embodiments, nitrogen agents 130 include nitrogen disassociatedfrom NF₃ or another suitable nitrogen containing gas that might or mightnot be part of a compound used to introduce the etchant (e.g.,fluorine). In certain embodiments, plasma 122 is generated from gasesthat include a hydrogen-containing gas (e.g., H₂ or NH₃), and hydrogenagents 128 include hydrogen disassociated from the hydrogen-containinggas.

In certain embodiments, plasma 122 is generated from gases that includeat least one noble gas, such as Ar, He, or Kr. As particular examples,plasma 122 may be generated from a gas combination that includes NF₃,NH₃, and Ar; NF₃, NH₃, N₂, and Ar; NF₃, H₂, and Ar; or NF₃, H₂, Ar, andN₂. In certain embodiments, passivation layer 124 formed on exposedsurfaces 118 of Si layers 110 includes Si nitride (e.g., Si₃N₄).

At step 308, substrate 102 (including film stack 104) is exposed toplasma 122 in plasma chamber 123. Plasma 122 causes passivation layer124, which may be a nitride layer, to be formed on exposed surfaces 118and additional surfaces 138 of Si layers 110. In certain embodiments,passivation layer 124 includes Si nitride (Si₃N₄). Plasma 122 alsoselectively etches exposed surfaces 116 (e.g., opposing exposed ends) ofGe-containing layers 108 to form indents 136 in Ge-containing layers 108relative to exposed surfaces 118 (e.g., opposing exposed ends) of Silayers 110. Passivation layer 124 inhibits etching of Si layers 110 byplasma 122. In certain embodiments, step 308 is an isotropic etchprocess.

At step 310, additional fabrication steps are executed. The discussionof potential additional processing steps described above with referenceto step 210 of FIG. 2 is incorporated by reference. At step 312, themethod ends.

FIG. 4 illustrates an example device 400 including a substrate with arecessed alternating film stack according to certain embodiments of thisdisclosure. At least a portion of device 400 may be formed using any ofthe processes and methods as described herein.

Device 400 includes a substrate 402 that includes a channel material 404(e.g., Si or SiGe) and a gate material 406, (e.g. Ge or SiGe). Channelmaterial 404 may correspond to Si layers 110 of substrate 102, at somepoint after process 100. Device 400 may be a GAA device as shown here ormay be any other device, such as a fin field-effect transistor (FinFET).Device 400 also may include isolation regions 408. In certainembodiments, isolation regions 408 are shallow trench isolations (STIs).

Device 400 may be fabricated by first forming a recessed alternatingfilm stack 410 (which may correspond to film stack 104 following process100, possibly with additional subsequent processes) and then depositingadditional gate material 406 over recessed alternating film stack 410.Specifically, device 400 may be formed by heteroepitaxial growth ofalternating Si and Ge or SiGe layers which are then patterned andrecessed vertically to expose the Si layers laterally.

The application of embodiments described herein may advantageously be anoptimal solution for the 5 nm node, 3 nm node, or lower. For example,the GAA device architecture may be suitable for scaling beyond the 7 nmnode. The GAA device architecture may address short channel effectsfound in some FinFET architectures by wrapping the gate around theentire channel instead of only three sides. This could reduce oreliminate current leakage occurring under the gate of the FinFET,therefore reducing non-active power losses.

FIG. 5 illustrates a block diagram of an example plasma tool 500,according to certain embodiments of this disclosure. Although aparticular plasma tool 500 is illustrated and described, any suitabletype of plasma tool may be used. Plasma tool 500 may be used to executeplasma step 120 described with respect to FIGS. 1A-1D and 2-4.

Plasma tool 500 includes plasma chamber 123 in which a semiconductorsubstrate (e.g., substrate 102) is processed using a plasma (e.g.,plasma 122). Plasma chamber 123 includes a substrate table 502configured to support substrate 102 during processing. In certainembodiments, substrate 102 is positioned on substrate table 502 in thecondition shown in FIG. 1B, following removal of barrier layer 114 forexample, for performing plasma step 120 using plasma 122. The materialof Ge-containing layers 108 (described above, for example, withreference to FIGS. 1A-1D) of film stack 104 of substrate 102 isselectively etched within plasma chamber 123 by injecting the plasma(e.g., plasma 122) through a shower head 504 of plasma tool 500. Showerhead 504 may include a single mixed reaction cavity that is filled withthe precursor gases, mixing gases, and carrier gases that mix to formplasma 122 and a set of exit holes for dispensing plasma 122 towardsubstrate 102.

Plasma chamber 123 includes and/or is otherwise coupled to a vacuum pump506 coupled to a vacuum line 508 to purge residual precursor gases fromplasma chamber 123 and also may include and/or otherwise be coupled to apressure system to maintain a target pressure in certain embodiments.Plasma chamber 123 may further include machine tools such as a heater510 and temperature sensor 512 used to heat substrate 102 and controlthe temperature within plasma chamber 123 and/or of substrate 102.

Plasma tool 500 includes a precursor gas line 514, a mixture gas line516, and a carrier gas line 518 coupled to shower head 504. In certainembodiments, the precursor gas fed through precursor gas line 514 mayinclude a fluorine-based precursor, such as NF₃ and/or SF₆, the mixturegas fed through mixture gas line 516 may include hydrogen (e.g., H₂ orNH₃), and the carrier gas fed through carrier gas line 518 may include anoble gas, such as Ar, He, or Kr.

In certain embodiments, plasma tool 500 may include a system of massflow controllers and sensors for control of gas flow (e.g., mass flowrate). Accordingly, plasma tool 500 may include a first flow controller520, a second flow controller 522, a third flow controller 524, vacuumpump 506, heater 510, temperature sensor 512, voltage-current (V-I)sensor 526, and substrate sensors 528, 530, 532, and 534 (528-534).Precursor gas line 514, mixture gas line 516, and carrier gas line 518are coupled to and controlled by first flow controller 520, second flowcontroller 522, and third flow controller 524, respectively.

Plasma tool 500 may include a controller 536 to control aspects ofplasma step 120. Controller 536 may be implemented in any suitablemanner. For example, controller 536 may be a computer. As anotherexample, controller 536 may include one or more programmable ICsprogrammed to provide functionality described herein. In a particularexample, one or more processors (e.g., microprocessor, microcontroller,central processing unit, etc.), programmable logic devices (e.g.,complex programmable logic device), field programmable gate array,etc.), and/or other programmable ICs are programmed with software orother programming instructions to implement functionality describedherein for controller 536. The software or other programminginstructions can be stored in one or more non-transitorycomputer-readable mediums (e.g., memory storage devices, flash memory,dynamic random access memory, reprogrammable storage devices, harddrives, floppy disks, DVDs, CD-ROMs, etc.), and the software or otherprogramming instructions when executed by the programmable ICs cause theprogrammable ICs to perform operations described herein.

Machine components such as heater 510 and temperature sensor 512 ofplasma chamber 123 as well as flow controllers 520, 522, and 524, vacuumpump 506, and other components external to plasma chamber 123 arecoupled to and controlled by controller 536.

Equipment sensors measure equipment parameters such as the temperatureof substrate table 502, heater currents, vacuum pump speed andtemperature, and provide signals to ensure the equipment is operatingproperly. Various process sensors measure process parameters such asprocess temperature, process pressure, plasma density, gas flow rates,and gas composition, and provide signals to ensure the process isoperating properly. The data from the equipment and process sensorsprovide feedback to controller 536 continuously throughout plasma step120. Controller 536 can make adjustments in real time to keep theequipment and process close to center of specifications.

Controller 536 receives data from the sensor(s) and controls processparameters of plasma chamber 123 based on the sensor data. Controller536 may analyze the data collected by the sensor(s), determine when tomodify or end one or more steps of plasma step 120, and provide feedbackto control process parameters of components of plasma chamber 123.

Controller 536 may be connected to V-I sensor 526, and substrate sensors528-534 to monitor plasma 122 as substrate 102 is exposed to plasma 122to provide conditions of plasma 122 as well as optionally compositionand thickness data in real time. This feedback data can be used bycontroller 536 to continuously adjust plasma step 120 as substrate 102is selectively etched using plasma 122 and, for example, to turn offplasma step 120 when the target indent (e.g., etched width 144) isreached.

Specifically, measurement data from substrate sensors 528-534, andtemperature sensor 512 may be received by controller 536 whilecontroller 536 generates control signals sent to first flow controller520, second flow controller 522, third flow controller 524, vacuum pump506, and heater 510.

Controller 536 may receive measurement or metrology data from substratesensors 528-534 taken at multiple points across substrate 102 to measureprocess uniformity and the thickness and composition of passivationlayer 124 (formed from exposure of substrate 102 to plasma 122), exposedend separation 142, and/or the target indent (e.g., etch width 144) insitu and in real time. For example, multiple across substrate sensors ina multi-substrate plasma tool can be used to monitor and tune thethickness and composition of passivation layer 124 (formed from exposureof substrate 102 to plasma 122), exposed end separation 142, and/or thetarget indent (e.g., etch width 144) from the top to the bottom of thesubstrate 102. Multiple across substrate sensors in a single substrateplasma tool can be used to monitor and tune the thickness andcomposition of passivation layer 124 (formed from exposure of substrate102 to plasma 122), exposed end separation 142, and/or the target indent(e.g., etch width 144) from the center of the substrate 102 to the edgeof the substrate 102.

Substrate sensors 528-534 may be coupled to and/or located within plasmachamber 123 for monitoring various parameters of substrate 102, plasmatool 500 and/or plasma step 120. Substrate sensors 528-534 may includevarious types of sensors including, but not limited to, optical sensors(such as cameras, lasers, light, reflectometer, spectrometers,ellipsometric, etc.), capacitive sensors, ultrasonic sensors, gassensors, or other sensors that may monitor a condition of substrate 102,plasma 122, and/or plasma tool 500. In certain embodiments, one or moreoptical sensors may be used to measure in real time (during plasma step120) the thickness and refractive index of the material at surfaces 118of Si layers 110 and surfaces of base layer 106 (e.g., where passivationlayer 124 is being formed), exposed end separation 142, and/or an etchedwidth 144 a (or another suitable measurement). As another example, aspectrometer may be used to measure in real time (during plasma step120) a film thickness of the material at surfaces 118 of Si layers 110and surfaces of base layer 106 (e.g., where passivation layer 124 isbeing formed), exposed end separation 142, and/or an etched width 144 a(or another suitable measurement). In yet another embodiment, a residualgas analyzer (RGA) may be used to detect in real time (during plasmastep 120) precursor breakdown for real-time chemical reaction completiondetection.

Controller 536 may receive user-input process parameters, including, forexample, etch rate, conformality, profile, and deposition rate (e.g., ofpassivation layer 124) based on standard plasma etch parameters such aschamber pressure, chamber temperature, RF source power, RF bias power,RF waveform (e.g., continuous wave RF, pulsed RF, square pulse, sawtoothpulse, and the like), etch time, and the composition and flow rates ofvarious process and carrier gases. Advantageously, allowing a user totune plasma 122 to meet a target local critical dimension uniformity(LCDU).

Based on data from substrate sensors 528-534 and the user inputtedprocess parameters, controller 536 generates control signals totemperature sensor 512 and heater 510 to adjust the heat within plasmachamber 123. As heater 510 heats plasma chamber 123, controller 536constantly or periodically monitors temperature sensor 512 to track thetemperature of plasma chamber 123 to send control signals to heater 510to maintain the temperature in plasma chamber 123.

Once controller 536 determines, based on data provided by temperaturesensor 512, that the target temperature of plasma chamber 123 has beenreached, controller 536 generates control signals and data signals toactivate first flow controller 520, second flow controller 522, andthird flow controller 524 and provide, based on the user-input processparameters, target flow rates of the precursor gas to first flowcontroller 520, a target flow rate of the mixing gas to second flowcontroller 522, and a target flow rate of the carrier gas to third flowcontroller 524. Once controller 536 determines that the correspondingflow rates are established, controller 536 provides power to plasmachamber 123 to power plasma 122 through bias and source electrodes.Based on the measurements from V-I sensor 526, the power being suppliedto the bias and source electrodes may be adjusted. First flow controller520, second flow controller 522, and third flow controller 524 each maybe a closed loop control system connected to a flow rate sensor and anadjustable proportional valve that allows each flow controller toconstantly or periodically monitor and internally maintain the targetflow rates of each gas via the flow rate sensor and the adjustableproportional valve.

In certain embodiments, once controller 536 determines, based on theuser inputted data, that the etch process time has been met, controller536 generates control signals to deactivate first flow controller 520,second flow controller 522, and third flow controller 524, which may bedeactivated at the same or different times, as may be appropriate.

Controller 536 may use or analyze substrate sensor data to determinewhen to end plasma step 120. For example, controller 536 may receivedata from a residual gas analyzer to detect an endpoint of plasma step120. In another example, controller 536 may use spectroscopicellipsometry to detect an average film thickness of passivation layer124, exposed ends 141 of Si layers 110, and/or exposed end separation142 during plasma step 120 and indicate changes during plasma step 120.In another example, controller 536 may use spectroscopic ellipsometry todetect the refractive index of the material at surfaces 118 of Si layers110 and surfaces of base layer 106 (e.g., where passivation layer 124 isbeing formed) during plasma step 120 and indicate film compositionchange during plasma step 120. Controller 536 may automatically endplasma step 120 when an exposed end separation 142 and/or an etchedwidth 144 a (or another suitable measurement) objective is achieved. Incertain embodiments, controller 536 may automatically adjust one or moreparameters such as the ratio of NF₃ to H₂ (or NH₃) and/or the ratio ofNF₃ to Ar, for example, during plasma step 120 to achieve the desiredetch profile of film stack 104. Controller 536 and the data fromsubstrate sensors 528-534 also may be used to achieve a desiredsemiconductor substrate throughput objective. Further, controller 536and the data from substrate sensors 528-534 may be used to achieve adesired etch profile of film stack 104 and composition along with adesired semiconductor substrate throughput or alternatively target acombination.

Although described for a particular application of formingnanowires/nanosheets for GAA devices, this disclosure may be used in anytype of isotropic etch of Si that is selective to Ge-containing layers.Furthermore, although the etch being performed is primarily described asbeing for forming indents in film stack 104 by removing portions ofopposing ends of Ge-containing layers 108, processes 100 and 400 may beused to remove substantially all portions of Ge-containing layers 108,which may be referred to as releasing Si layers 110.

Although this disclosure describes particular process/method steps asoccurring in a particular order, this disclosure contemplates theprocess steps occurring in any suitable order. While this disclosure hasbeen described with reference to illustrative embodiments, thisdescription is not intended to be construed in a limiting sense. Variousmodifications and combinations of the illustrative embodiments, as wellas other embodiments of the disclosure, will be apparent to personsskilled in the art upon reference to the description. It is thereforeintended that the appended claims encompass any such modifications orembodiments.

1. A method for processing a semiconductor substrate, the methodcomprising: receiving a semiconductor substrate that comprises a filmstack, the film stack comprising a first silicon layer, a second siliconlayer, and a first germanium-containing layer positioned between thefirst silicon layer and the second silicon layer; and selectivelyetching the first germanium-containing layer by exposing the film stackto a plasma comprising fluorine agents, nitrogen agents, and hydrogenagents, the plasma etching the first germanium-containing layer whilesimultaneously causing a passivation layer to be formed on exposedsurfaces of the first silicon layer and the second silicon layer toinhibit etching of the first silicon layer and the second silicon layerduring exposure of the film stack to the plasma, the passivation layercomprising nitride.
 2. The method of claim 1, wherein the plasma isgenerated from gases comprising a noble gas.
 3. The method of claim 1,wherein the plasma is generated from gases comprising nitrogentrifluoride (NF₃) gas, the fluorine agents comprising fluorinedisassociated from the NF₃ gas.
 4. The method of claim 1, wherein theplasma is generated from gases comprising H₂ gas, the hydrogen agentsbeing hydrogen.
 5. The method of claim 1, wherein the plasma isgenerated from a gas combination comprising: nitrogen trifluoride (NF₃),ammonia (NH₃), and argon (Ar); NF₃, NH₃, nitrogen (N₂), and Ar; NF₃,hydrogen (H₂), and Ar; or NF₃, H₂, Ar, and N₂.
 6. The method of claim 1,wherein the passivation layer formed on the exposed surfaces of thefirst silicon layer and the second silicon layer comprises siliconnitride.
 7. The method of claim 1, wherein the firstgermanium-containing layer is a silicon-germanium (SiGe) layer thatcomprises about fifty percent or less germanium.
 8. The method of claim7, wherein: the first germanium-containing layer comprises less than orequal to about fifteen percent germanium; and selectivity of the firstgermanium-containing layer to the first and second silicon layers isgreater than or equal to about 70:1.
 9. The method of claim 1, whereinselectively etching the first germanium-containing layer comprisesselectively etching an end portion of the first germanium-containinglayer to form an indent in the film stack between the first siliconlayer and the second silicon layer.
 10. The method of claim 1, wherein,as the first germanium-containing layer is selectively etched,additional surfaces of the first silicon layer and the second siliconlayer are exposed, the plasma forming the passivation layer on theadditional surfaces.
 11. The method of claim 1, wherein selectivelyetching the first germanium-containing layer comprises selectivelyremoving substantially all of the first germanium-containing layerbetween the first silicon layer and the second silicon layer.
 12. Themethod of claim 1, wherein, prior to selectively etching the firstgermanium-containing layer: a native oxide layer is present on a surfaceof the film stack; and the method further comprises etching the nativeoxide layer.
 13. The method of claim 1, wherein: the film stack furthercomprises a second germanium-containing layer and a third silicon layer,the second germanium-containing layer positioned between the secondsilicon layer and the third silicon layer; and the method comprisesselectively etching the second germanium-containing layer by exposingthe film stack to the plasma, the plasma forming the passivation layeron exposed surfaces of the third silicon layer to inhibit etching of thethird silicon layer during exposure of the film stack to the plasma. 14.A method for processing a semiconductor substrate, the methodcomprising: positioning a semiconductor substrate in a plasma chamber ofa plasma tool, the semiconductor substrate comprising a film stack thatcomprises silicon layers and germanium-containing layers in analternating stacked arrangement, with at least two silicon layers and atleast two germanium-containing layers; generating, in the plasma chamberof the plasma tool, a plasma that comprises fluorine agents, nitrogenagents, and hydrogen agents, the plasma being generated from gasescomprising a fluorine-containing gas, a nitrogen-containing gas, ahydrogen-containing gas, and a noble gas; and exposing, in the plasmachamber of the plasma tool, the film stack to the plasma, the plasmacausing a nitride passivation layer to be formed on exposed surfaces ofthe silicon layers and selectively etching opposing exposed ends of thegermanium-containing layers to form indents in the germanium-containinglayers relative to opposing exposed ends of the silicon layers, thenitride passivation layer inhibiting etching of the silicon layers bythe plasma.
 15. The method of claim 14, wherein: the fluorine-containinggas comprises nitrogen trifluoride (NF₃), sulfur hexafluoride (SF₆), orcarbon tetrafluoride (CF₄); and the fluorine agents comprise fluorinedisassociated from the fluorine-containing gas.
 16. The method of claim14, wherein: the hydrogen-containing gas comprises H₂ or ammonia (NH₃);and the hydrogen agents comprise hydrogen disassociated from thehydrogen-containing gas.
 17. The method of claim 14, wherein: thenitrogen-containing gas comprises N₂, nitrogen trifluoride (NF₃) orammonia (NH₃); and the nitrogen agents comprise nitrogen disassociatedfrom the nitrogen-containing gas.
 18. The method of claim 14, wherein:the nitrogen-containing gas and the fluorine-containing gas are part ofa same gas compound; or the nitrogen-containing gas and thehydrogen-containing gas are part of a same gas compound.
 19. The methodof claim 14, wherein: a flow rate of the noble gas is greater than aflow rate of the fluorine-containing gas; and the flow rate of thefluorine-containing gas is greater than a flow rate of thehydrogen-containing gas.
 20. The method of claim 14, wherein the noblegas is argon (Ar).
 21. The method of claim 14, wherein the gases fromwhich the plasma is generated comprise: nitrogen trifluoride (NF₃),ammonia (NH₃), and argon (Ar); NF₃, NH₃, nitrogen (N₂), and Ar; NF₃,hydrogen (H₂), and Ar; or NF₃, H₂, Ar, and N₂.
 22. The method of claim14, wherein the nitride passivation layer formed on the exposed surfacesof the silicon layers comprises silicon nitride.
 23. A method forprocessing a semiconductor substrate, the method comprising: positioninga semiconductor substrate in a plasma chamber of a plasma tool, thesemiconductor substrate comprising a film stack that comprises firstlayers of a first material and second layers of a second material in analternating stacked arrangement, the first material being agermanium-containing material that includes germanium at a concentrationof about ten to about fifty percent; generating a plasma for selectivelyetching the first layers of the first material, generating the plasmacomprising introducing gases including fluorine, nitrogen, hydrogen, anda noble gas into the plasma chamber and maintaining a pressure in theplasma chamber of less than about 50 millitorr; and exposing, in theplasma chamber, the film stack to the plasma for a time period, theplasma causing a nitride passivation layer to be formed on exposedsurfaces of the second layers of the second material and selectivelyetching opposing exposed ends of the first layers of the first materialto form indents in the first layers of the first material relative toopposing exposed ends of the second layers of the second material.
 24. Amethod for processing a semiconductor substrate, the method comprising:receiving a semiconductor substrate that comprises a film stack, thefilm stack comprising a first silicon layer, a second silicon layer, anda first germanium-containing layer positioned between the first siliconlayer and the second silicon layer; and selectively etching the firstgermanium-containing layer by exposing the film stack to a plasmacomprising fluorine agents, nitrogen agents, and hydrogen agents, theplasma etching the first germanium-containing layer while simultaneouslycausing a passivation layer to be formed on exposed surfaces of thefirst silicon layer and the second silicon layer to inhibit etching ofthe first silicon layer and the second silicon layer during exposure ofthe film stack to the plasma.